1. Field of the Invention
The present invention relates in general to a wastewater decanter and, more particularly, but not by way of limitation, to a valveless siphon decanter which can substantially exclude solids and can be retrofit into existing sequencing batch reactor systems to replace current wastewater decanters.
2. Background Art
The treatment of wastewater is well known in the art. Commonly, sequencing batch reactors or SBRs are used to process wastewater and can include two or more processing tanks. SBRs treat wastewater such as sewage or output from anaerobic digesters or mechanical biological treatment facilities in batches. The tanks have a “flow through” system, with raw wastewater (influent) entering through an inlet and treated fluid (effluent) flowing out the other. While one tank is in settle/decant mode the other may be aerating and filling. At the inlet is a section of the tank known as the bio-selector. This consists of a series of walls or baffles which direct the flow either from side to side of the tank or under and over consecutive baffles. The walls or baffles help to mix the incoming influent and any returned activated sludge, beginning the biological digestion process before the wastewater enters the main part of the first tank.
Typically, there are five stages in the treatment of wastewater including filling the tank, reacting the wastewater with biological agents, allowing the solids to settle from the wastewater, drawing the treated fluid from the first tank and idling the removed fluid in a second tank. Aeration of the mixed wastewater is performed during the first two stages by the use of fixed or floating mechanical pumps or by blowing it into finely perforated membranes fixed to the floor of the tank. During this period the inlet valve to the tank is open and a returned activated sludge pump takes mixed liquid and solids (mixed liquor) from the outlet end of the tank to the inlet to “seed” the incoming sewage with live bacteria.
After the step of settling, the wastewater is stratified such that the solids are disposed at the bottom of the tank, a mixture of solids and biological agents are disposed above the solids, and a level of cleaner fluid is disposed at the surface of the tank. Currently, the step of drawing the cleaner fluid from the first tank is facilitated by the use of something such as a floating decanter. While wastewater decanters are well known, they suffer from common drawbacks including, but not limited to, portions of the decanter being disposed underneath the fluid leading to unnecessary and costly maintenance thereof and unwanted removal of solids from the reactor which can cause fouling of the decanter and thus increased maintenance. Common decanters include a gravity inlet orifice supported above or below the fluid by a flotation device. The gravity inlet orifice is connected to a tubular boom or outlet pipe that extends from near the bottom of the tank and angles upwardly towards the cleaner fluid such that the gravity inlet orifice is disposed just below the surface of the fluid.
Therefore the need exists for a valveless siphon decanter for use in wastewater reactors that substantially excludes solids during operation thereof, and furthermore to a valveless siphon decanter which can be installed through or over the tank in such a way that none of the parts of the decanter are submerged under the wastewater contained within the reactor.